In a new fuel bundle designed by the assignee of the present invention, mechanical support for the bundle is provided by a pair of central water rods connected to the lower tie plate rather than by conventional tie rods. Each of the water rods comprises a pair of separate assemblies. The lower assembly in each rod comprises a central tube while the upper assembly includes a tie bar. The central tube and the tie bar are adjustably secured to one another by a mechanism not forming part of the present invention but which results in water rods having adjustable lengths. The adjustment is provided by relative axial movement of the central tube and the tie bar which, when adjusted, provide a water rod of fixed length. In this design, and because the fuel bundle is supported at the top by the pair of water rods rather than by tie rods, the overall lengths of the two water rods must be closely matched to prevent tilting or excessive stress on the tie bars. The lengths of each rod from the top face of the lower tie plate to the opposite end of the rod must lie within a very narrow range of tolerances relative to one another, for example on the order of 0.020 inches and must correspond substantially exactly to a predetermined length of the water rod e.g. within 0.040 inches. It will be appreciated that fuel bundles are typically assembled with the bundle lying in a horizontal position which, after assembly, is lifted to a vertical position. That movement as well as other assembly procedures cause stresses in the fuel bundle which can alter the length of the water rods after they have been initially adjusted in length. It is essential that the water rods lie within specific design length limits when the fuel bundle is shipped to the operational site.